Contreras, Dori , Upchurch, Garland , Mack, Greg .
New data on the structure and phylogenetic position of an extinct Cretaceous redwood.
The evolutionary history of redwoods (Sequoioid clade of the Cupressaceae) is currently unresolved by both molecular and fossil data, particularly in regards to the patterns of character evolution and the order of divergence of taxa. These investigations have been complicated by the antiquity of the lineage and extinctions, with modern genera representing relics of a once much larger group. Previously, we reconstructed an extinct Late Cretaceous redwood from the Jose Creek Member, McRae Formation of New Mexico based on associated shoot impressions, pollen cones, and in situ permineralized stump. Here we test earlier interpretations of pollen cone structure using X-ray micro-tomography, expand comparisons with extant Cupressaceae s. lat., and consider the relationship of the Jose Creek redwood to living and well-characterized fossil redwoods. The shoot impressions (preserving up to three orders of branching) show that the thickest branches bear highly reduced (scale-like) leaves and give rise to planate branchlets bearing elliptic bifacially flattened leaves with acute apices and decurrent attachment to the stem, as in Sequoia. However, they exhibit opposite decussate leaf arrangement, rotated into one plane with zig-zag leaf bases as in modern and fossil Metasequoia. The associated pollen cones are ellipsoid with peltate microsporophylls, each bearing three abaxial ovoid microsporangia, as in Sequoia and Sequoiadendron. They are shed singly, either attached to the tip of a reduced shoot with scale-like leaves or with only their subtending bud scales, suggesting both terminal and subterminal axillary positioning, as in Sequoia. X-ray micro-tomography of pollen cones confirms the helical arrangement of microsporophylls, the rhomboidal shape of the distal lamina, and eccentric attachment of lamina to the stalk. The Jose Creek redwood differs from all living species of redwoods in the absence of scale leaves at the base of the branchlets and the absence of growth rings in the wood, suggesting absent or poorly developed dormancy mechanisms. In order to evaluate the systematic significance of the preserved characters we conduct a phylogenetic analysis of extant basal Cupressaceae, representatives of the Cupressoideae and Callitroideae, and select fossil redwoods. Our taxon nests below a well-defined clade formed by Metasequoia and Parataxodium. Its exact position relative to other sequoioid conifers is discussed, based upon interpretation of certain characters. The Jose Creek redwood possesses a novel combination of characters that expands our knowledge of the past diversity and ecology of redwoods, and enables further insight into the pattern of character evolution for the Sequoioideae.
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1 - University of California-Berkeley, Department of Integrative Biology and Museum of Paleontology, 3060 Valley Life Sciences Bldg #3140, Berkeley, CA, 94720, USA
2 - Texas State University, Department of Biology, 601 University Drive, San Marcos, TX, 78666, USA
3 - New Mexico State University, Department of Geological Sciences, P.O. Box 30001, Las Cruces, NM, 88003
Cupressaceae s. lat.
Presentation Type: Oral Paper:Papers for Sections
Location: Melrose/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 11:15 AM
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award